Embodiments of the present invention provide a sensor arrangement as it may, for example, be used in combination with Hall sensors. Further embodiments provide a method which may, for example, be used in combination with Hall sensors.
Basically, the offset of a sensor and that of a subsequent amplifier are determined or compensated separately from the useful signal, as otherwise an unknown value of the measurement is overlaid which is at best constant but mostly depends on the temperature. In the measurement of very small signals, the offset signal may well be a magnitude above the useful signal. So that stochastic interference signals existing in further processing have little influence on the measurement and remain small as compared to the useful signal, the useful signal is highly amplified directly after the sensor. If the offset signal is too large, however, the amplifier is driven into confinement by this offset signal and the useful signal can no longer reach the subsequent processing chain. In the following, some concepts for offset compensation are to be presented.    1. Offset compensation by addition/subtraction of a digitally controlled signal after the amplifier.            There are circuits which first of all amplify the signal a little in order to then subtract a correction voltage. Then, a further amplifier stage follows. The sensor signal is not deteriorated before amplification. By the overload conditioned by the offset only small amplifications are possible.        A somewhat better method is illustrated by DE 10 2004 010 362 B4 or by DE 10 2009 006 546 A1. An amplifier having a current output is illustrated whose output current is summed up with a current from a digitally tracked DAC. The compensation is independent of the internal resistance of the sensor but the problem of the possible overload with a small sensor signal remains. Current circuits do have a higher dynamic range that voltage circuits, but this procedure is not optimal in particular with high amplifications. Apart from that, current outputs are usually not as linear and, in the amplification factor, not as temperature-stable as voltage outputs.        A very high amplification of a sensor signal is not possible in this way.            2. Offset compensation by addition or subtraction of a digitally controlled signal before the amplifier.            US 2003/0178989A1 shows the application of a summator circuit before the amplifier. By this, the amplifier can no longer be overdriven or overloaded by the offset. The adder circuit is, however, located in the noise- and distortion-sensitive part of the circuit, and is thus the main source for stochastic interferences and non-linear distortion. A highly accurate system cannot be acquired in this way.            3. Offset compensation in the sensor by a determined feed of a temperature-dependent current.            EP 0525235 describes how a compensation current is realized, depending on the temperature, with constant and settable linear and square portions which are set once upon manufacturing for each sensor system. In this example, this serves to shift the time of a comparator downstream from the sensor by a very large but temperature-constant amount as not the sensor, but a continuously existing external magnetic field is to trigger a switchover only when exceeding this amount. Influences on the offset of the sensor beyond this temperature remain uncompensated like, for example, the change of the temperature characteristic over time.        The necessity for calibration with different temperatures is time-consuming and expensive.        